Sensitive flip-flop circuit



'Nov. 14, 1950 G. J. SCOLES 2,530,033

SENSITIVE FLIP-FLOP CIRCUIT Fixedjan. so. 1948 g I HT+ SYN II IfIhventor': Graham J. Scales,

bym D 7774m 4 His Attorney.

Patented Nov. 14, 1950 SENSITIVE FLIP-FLOP CIRCUIT Graham J. Scoles,London, England, assignor to General Electric Company, a corporation ofNew York Application January 30, 1948, Serial No. 5,356 In Great BritainFebruary 19, 1947 6 Claims.

This invention relates to flip-flop, or Eccles- "Jordan circuits of thekind in which a primary valve upon receipt of a synchronizing signalapplies a negative potential to the grid of a secondary valve so as todrive the secondary valve from the conducting to the non-conductingstate, in which state it remains until the negative charge on thecontrol grid leaks away sufficiently to render it once more conducting.More'particularly the invention relates to a feedback arrangement insuchcircuits whereby the secondary valve is "conditioned for actuation by arelatively small triggering signal to return to the conductive state.

The time period during which the secondary valve is in thenon-conducting state depends upon the time constant of the leakagecircuit to the "control grid and is predeterminable by suitable choiceof the constants of the circuit. In certain applications, such as in thecontrol of time base circuits which have to cover'a wide range of sweepduration, it is convenient to make the time constant of the dischargecircuit long and to ter- -minate the time period bythe application of atriggering signal. Since the grid of the second- --ary valve willnormally be driven well past cut-off a large triggering signal isusually required.

The main object of the invention is to enable substantially the sameresult to be obtained with a relatively smaller triggering signal.

'According to the present invention, feedback is arranged between theanode and control grid of the secondary valve such that shortly afterinitial tripping the positive-going anode potential is applied to thecontrol grid of the secondary valve so as partially to counteract thenegative-going potential from the primary valve and hence reduce theextent by which the secondary valve is driven beyond cut-off. It will beappreciated that with such an arrangement only a, relatively smalltriggering signal is required to render the secondary valve once againconducting and to terminate the time period.

In carrying out the invention in the case of a cathode coupled flip-flopcircuit having the anode of the primary valve coupled through acondenser with the control grid of the secondary valve, a resistance maybe connected between the anodes of the primary and secondary valves toprovide the feedback and a capacitance connected between the anode ofthe secondary valve and earth.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. My inventionitself, however, both as to its organization and Fig. 3 illustrates thepotential wave forms in Figs.

1 and 2. i

Referring to Fig. 1, V1 is the primary valve above referred to and V2the secondary valve.

Fig. 1 shows an arrangement in which V2-'is normally conducting so thatthe voltage drop through the common cathode resistor R3 is suflicient tocut-ofi' the valve V1. going signal is applied to the terminal SYN thiswill be applied through 0'1 to the grid or control electrode of V2. Thiswill reduce the current through V2 and hence the voltage drop across R3.V1 accordingly conducts so that its anode voltage falls and increasesthe effect so that the action becomes cumulative and rapidly results inV1 conducting with V2 cut-off. The circuit will remain in this conditionfor a time determined mainly by the values of C1 and R2, and theamplitude of the excursion of the grid of V2 relative to its cathode.After such time delay V2'Will again become conducting and the circuitwill reset to its initial condition. In certain applications, such as inthe case of time base circuits which have to cover a wide range of sweepduration, it is convenient to make R2 and C1 very large and to terminatethe cycle by the application of a triggering signal applied for exampleacross R3 as described in my application for United States LettersPatent Serial No. 5,357 filed of even date herewith. This normally meansthata relatively large triggering signal is required as the grid of V2is usually driven Well past cut-off with the arrangement describedabove. In the arrangement of Fig. 2 a condenser C2 is connected betweenthe anode of V2 and earth, while a resistance R5 is connected betweenthe anodes of V1 and V2. Suppose now a negative-going signal is appliedto the terminal SYN. This as above described will trip the circuit.I-Icwever, due to the effect of C2 the anode potential at V2 will notinitially vary. The cessation of current through V2 Will allow C2 tocharge mainly through R4 with If now a negativeonce again conducting.These effects are illustrated in Fig. 3 in which the full line indicatesthe potential at the grid of V2 with the arrangement of Fig. 2, whilethe chain-dotted line represents the potential variation which occurswith the normal arrangement of Fig. l. The line OX represents the.normal cut-ofl potential for the grid of V2. The synchronizing pulse isapplied at the point a whereupon the grid potential immediately assumesa large negative value falling away slightly to the point D where thesynchronizing pulse terminates. With the normal arrangement of Fig. 1this negative value will remain until a triggering signal is applied,say at the point I, when the potential will rise until the cut-oil lineOX is reached, when the potential Will rise rapidly to the originalvalue at d.

It will be appreciated with this arrangement that a relatively largetriggering signalis required. With the arrangement of Fig. 2, however,the grid potential will, as shown bythe full line, rapidly rise to avalue just below the cutoff potential OX so that a much smallertriggering signal is required. If the triggering signal is applied atthe point k, which has for convenience been taken as the point where thetwo characteristicsintersect, the potential will again rise :to thelevel of OX and then rapidly to the point dthough clearly a much smalleramount of drive, that is, a smaller triggering signal, is 9 requiredthan in the previous example.

In Fig. 2 the anode of V1 is connected through a condenser C3 tothe'controlgrid of a pentode valve V3 which acts as the dischargingvalve for time base'condenser C4. It will be appreciated, however, thatthis is only an example of the application of .theinvention. Preferably.Rr and R5 in parallel are made equal to the value normall-ychosen forHim the absence 'of R5 so that thesensitivityto trip is notsubstantially altered.

In certain applications it is desirable for the waveform at the anode ofV2 to be as square as possible-and this 'is of course distorted by thepresence of C2. In such a case the invention may be modified by makingR5 in two portions with.-

Cz'joined between the junction of the two portions and suitable point ofreference, such as HT-, or earth. 7

While I have shown only certain preferred embodiments of my invention byway of illustration, 'many modifications will occur to those skilled inthe art and I therefore wish to have it understood that I intend, in theappended claims, to cover all such modifications as fall within the truespirit and scope of my invention.

.What I claim as new and desire to secure by Letters Patent of theUnited States is:

l. A flip-flop circuit comprising a pair of electron discharge devices,each with an anode, a cathode and a control electrode, biasing means fora first one of said devices for biasing said first device tonon-conduction during conduction of thesecond of said devices, saidmeans comprising a common cathode impedance for said cathodes, a longtime constant control electrode circuit for said second device connectedto the anode of said first device, whereby application of asynchronizing signal to said second device which tends to reduceconduction in said sec- -ond device causes conduction of said first de-'vice, av resistor directly interconnecting said anodes, and a capacitorconnected directly from a point of fixed potential to a point on saidresistor.

2.;Acathode coupled flip-flop circuit with a first and a second electrondischarge device, each of said devices having an anode, a cathode and acontrol electrode, said devices having a common cathode impedance fordeveloping a cutoff biasing potential for either of said devices whenthe other is conducting, said second device being normally conductive,an anode load impedance for each of said respective devices, a capacitorconnecting the anode of the first device to the control electrode of thesecond device for applying a cut-off impulse thereto, and means forslowly discharging said capacitor, said circuit being characterized by aresistor connect- .ing said respective anodes and a capacitorconcapacitor coupling the anode of the first of'sa'id devices to thecontrol electrode of the second device, *a control electrode leakresistor for said second device, a common cathode impedance for said twodevices, the control electrode of said second device being arranged toreceive an impulsetending to reduce conduction 'of'saidisecond device,whereby reception .of said impulse :causes conduction of said firstdevice to provide a negative potential through said capacitor tothe-control electrode of said second device, and feedback means forlimiting the efiect of said negative potential, said means comprising aresistor interconnecting said anodes and a capacitor connected between apoint on said resistor removed from the anode of said first device and apoint inrsaid circuit at which the potential varies to a lessextent'than at the anode of-said first device.

4. A flipflop circuit comprising a firsttanda second discharge device,each with an anode,.sa control'electrodeand a cathode, :means for bias-:ing said first device'to a non-conductive condition, 'said'meanscomprising said second device and being responsive to current flowthere-- through, said second device being arranged .to receive a currentreducing impulse 'to disable said means to cause said first device toconduct, an anode resistor for each of said devices, means coupling theanode of said first device to the control electrode of said seconddevice for further reducing the current in said second device inresponseto conduction of said first device, and a feedback network forpartially overcoming the effect of said last means a predetermined timeafter the reduction of current in said second device, said networkcomprising an energy storage device and means 'for storing energy insaid energy storage device which is principally a function of thepotential of the anode of the second device and means for furnishing aportion of said energy to the anode of said first device.

5. A cathode coupled flip-flop circuit with-a first and a secondelectron discharge device, each of said deviceshaving an anode, acathode'and a control electrode, said devices having a common cathodeimpedance fordeveloping a cut-01f biasing potential for either of saiddevices when the other is'conducting, said second device beingnormallyconductive, an anode load impedance-for each of said'respective devices,a capacitor "connecting the anode of the first device to the controlelectrode of the second'device foraapplying a cut-off impulse thereto,means for slowly-discharging said capacitor, and a network forrelatively rapidly reducing the intensity of said impulse after thestart thereof thereby to condition said second device to receive a smalltriggering signal to become conductive again, said network comprising acapacitor having one terminal thereof connected to the anode of saidsecond device and the other terminal thereof connected to a relativelyfixed potential point, said capacitor chargeable through the anode loadimpedance of said second device and means for providing at least aportion of said charge to the anode of said first device.

6. A fiip-fiop circuit comprising a pair of electron discharge devices,each with an anode, a

cathode and a control electrode, biasing means for a first one of saiddevices for biasing said first device to non-conduction duringconduction of the second of said devices, said means comprising a commoncathode impedance for said cathodes, a long time constant controlelectrode circuit for said second device connected to the first device,whereby application of a synchronizing signal to said second devicewhich tends to reduce conduction in said second device causes conductionof said first device, and a feedback anode of said network which tendsto increase the anode potential of said first device after said seconddevice becomes non-conductive comprising a capacitor having one terminalthereof connected to the anode of said second device and the otherterminal thereof connected to a relatively fixed potential point, saidcapacitor chargeable through the anode load resistor of said seconddevice and means connected to provide at least a portion of thepotential of said capacitor to the anode of said first device.

GRAHAM J. SCOLES.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,365,583 Nagel et a1 Dec. 19,1944 2,414,486 Rieke Jan. 21, 1947 2,416,333 Lehmann Feb. 25, 19472,441,579 Kenyon May 18, 1948 2,459,852 Summerhayes Jan. 25, 19492,470,028 Gordon May 10, 1949

